In an existing communications system (for example, a Long Term Evolution system), a terminal device sends uplink data based on a scheduling request mechanism shown in FIG. 1. When determining that there is uplink data to be sent, the terminal device may send an uplink scheduling request to a network device. The uplink scheduling request carries identification information (for example, a cell radio network temporary identity, or C-RNTI) of the terminal device. After receiving the uplink scheduling request, the network device may allocate an uplink transmission resource to the terminal device according to current system resource usage, and send an uplink grant (or UL grant) to the terminal device. The terminal device may send the uplink data to the network device on a transmission resource indicated by the uplink grant. As such, the network device may receive, on the corresponding transmission resource, the uplink data sent by the terminal device.
With the development of the Internet of Things (IoT), an increasing quantity of machine type communication (MTC) services emerge. Generally, a data packet transmitted in an MTC service is relatively small, and a transmission latency is also required to be small. When there is a large quantity of MTC services, the foregoing scheduling request mechanism not only brings a large quantity of signaling overheads, but also increases the transmission latency.
To resolve the foregoing problem, grant-free transmission has been proposed. Grant-free transmission means that a terminal device directly transmits uplink data to a network device without needing to request, in a scheduling request manner, a base station to allocate a transmission resource. In this case, the terminal device does not send an uplink scheduling request to the network device before sending the uplink data, and the network device therefore does not send a grant to or allocate a resource to the terminal device. Instead, the network device decodes the received uplink data in a blind detection manner. Therefore, the network device does not know which terminal device sends the detected uplink data.
Based on the foregoing problem, in grant-free transmission, the terminal device needs to add an identifier of the terminal device to an uplink data packet sent to the network device. However, in a scenario (e.g., IoT scenario) of massive accesses to a single cell in the future, there may be a large quantity of terminal devices, and the terminal device identifier used to identify each terminal device may be quite lengthy. For example, to support 300,000terminal devices in a single cell, a terminal device identifier needs to be at least 19 bits long. However, a data packet transmitted by a terminal device in this scenario may be relatively small. For example, a data packet in the IoT scenario is generally 100 bits to 1,000 bits long. In this case, if a terminal device identifier is carried in the data packet, a proportion of resources occupied by the 19-bit terminal device identifier in the entire data packet is approximately up to 16%. If the terminal device divides the data packet into smaller data packets for multiple transmissions, the proportion of resources occupied by the terminal device identifier becomes higher.